This puzzle involves a standard Sudoku X problem, with 1 to 9 appearing once in every row, column, 3x3 cell block and the two diagonals. While no starting numbers are provided here (again), the numbers around the grid represent the sum of the 'height' values for every visible building when viewed inwardly along the respective row, column and diagonal. For example, an indicated '11' would mean the first few cells could only be occupied by buildings having a unit height (e.g. storeys) of either 2 and 9, or 2, 1 and 9.